Problem: On the first 4 quizzes of her chemistry class, Vanessa got an average score of 86. What does she need on the next quiz to have an overall average of 88?
Let her score on the next quiz be $x$ The sum of all of her scores is then $4 \cdot 86 + x$ The same sum must also be equal to $5 \cdot 88$ Solve: $x = 5 \cdot 88 - 4 \cdot 86 = 96$.